The present invention relates generally to fluid circuits, and more particularly to a fluid control system for powering vehicle accessories such as a cooling fan and a power steering unit.
Many vehicles such as cars and trucks include a hydraulic-assisted steering linkage. These vehicles also include an engine cooling fan driven by a hydraulic motor. For economic reasons, it is known to provide an integrated fluid control circuit in these vehicles which includes both a fluid control circuit for operating an engine cooling fan, and a fluid control circuit for operating a hydraulic-assisted steering linkage. Such integrated fluid control circuits provide the necessary operational pressure for proper functioning of the fluid circuit with a single fluid pump. The use of a single fluid pump reduces costs associated with manufacturing the vehicle.
It is desirable to position the fluid components associated with the engine cooling fan in a series configuration with the fluid components associated with the hydraulic-assisted steering linkage. Such a series configuration creates a first pressure drop across the fluid components associated with the engine cooling fan and a second pressure drop across the fluid components associated with the hydraulic-assisted steering linkage. Such a configuration defines an integrated fluid control circuit wherein an output pressure on a fluid supply line of the single fluid pump fluctuates (i.e. rises and falls) as a function of the sum of the two pressure drops.
The pressure drop across each of the two groups of fluid components may vary widely depending on operating conditions associated with the vehicle. For example, on hot days the fluid pressure requirements associated with the engine cooling fan will increase. If during such a hot day the operator of the vehicle executes a steering maneuver that requires a large amount of fluid pressure (e.g. an abrupt, sharp turn), the sum of the two fluid pressure requirements may exceed the fluid pressure generating capabilities of the single fluid pump.
In such situations as described above wherein the fluid pressure requirements of the two groups of fluid components exceeds the pressure generating capabilities of the single fluid pump, it is desirable to give priority to the fluid components associated with the hydraulic-assisted steering linkage over the fluid components associated with the engine cooling fan. In particular, it is desirable to bypass fluid pressure around the fluid components associated with the engine cooling fan and direct the fluid pressure to the fluid components associated with the hydraulic-assisted steering linkage thereby reducing the speed of the engine cooling fan.
In addition, it is also desirable to control the overall fluid pressure of the integrated fluid control circuit. In particular, it is desirable to provide fluid pressure necessary to operate the fluid components associated with the engine cooling fan and the hydraulic-assisted steering linkage while not exceeding the operative range of the pressure generating capabilities of the single fluid pump.
What is needed therefore is an apparatus and method that gives priority to the advancement of fluid pressure to the fluid components associated with the hydraulic-assisted steering mechanism over the fluid components associated with the engine cooling fan which also controls the overall pressure associated with the integrated fluid control circuit.